As computers have become more complex, user interfaces have had to adapt to allow the user to control the operations of the computer. Initially, the interface used was a command line interface, which utilized a series of typed commands formatted in a specific syntax familiar to the computer and eventually learned by computer users. This interface was eventually replaced by the Graphical User Interface (“GUI”), which allows users to point to objects, buttons, and windows displayed like items on a desk. Initially, interaction between the GUI and a user was accomplished through a light pen, a pen-based computer control requiring the user to select and highlight objects on the screen by touching the light to the object on the screen. However, this implementation had its disadvantages because, by design, the user's hands and the light pen would obscure a portion of the screen from the user's own view. This and other disadvantages led to the development of the mouse, an interface control separate from the keyboard, that controlled a pointer on the GUI for selecting and highlighting objects, buttons, and windows.
The growth of the personal digital assistant (“PDA”) and wearable computer markets are associated with similar problems realized in the larger-scale computing systems. As PDA technology continues to rapidly advance with respect to the size of PDA electronics and batteries, the size of handheld and mobile devices becomes more dependent upon the user interface utilized.
The current most practiced method of interaction between a user and a personal digital assistant (“PDA”) is a stylus-based GUI. In stylus-based interaction, the user holds the device in one hand and the stylus in the other. A stylus-based GUI enables a user to take full advantage of the PDA by allowing the user to navigate through applications operating on a computing system, control operations associated with those applications, and input text while using only one selection device—the stylus. In short, a separate keyboard or other input device is not needed.
While such interaction is similar to the use of a conventional pad and paper, it is not without problems. Since the stylus-based GUI is a simple derivation of the former light pen, it includes many of the same problems associated with the light pen-based GUI's. The use of a stylus obscures the portion of the display that the writing hand is covering. Further, the stylus-based GUI requires two-hand operation and typically requires the user to look at the device while using it. The stylus-based GUI must also include complex software to recognize the user's handwriting.